1. Field of the Invention
The present invention pertains to flow meters, and in particular to flow meters for use with positive displacement pumps.
2. Description of the Related Art
Positive displacement pumps are currently being used in a variety of industrial and other applications. For example, U.S. Pat. No. 4,160,626 discloses a positive displacement pump of a type useful for water flooding of oil wells so as to augment the recovery of oil from producing well. Such pumps may be operated by high pressure air, natural gas or other fluid pumping media.
Frequently, it is desirable in pumping operations to introduce one or more chemical additives into the fluid being pumped. Such additives may, for example, comprise a viscosity enhancer useful for improving the pumping efficiency. Other additives may, for example, reduce foaming of the fluid being pumped. Frequently , the use of such chemical additives is important to maintain the regular operation of a producing well, and to reduce costly downtime. Many of these chemical additives are quite expensive, and considerable cost savings can be realized if overuse of the chemicals is eliminated. An accurate and reliable metering is needed to insure that the proper amount of chemical additives are injected, necessary to achieve the desire objective and to eliminate the usage of additional amounts of these chemicals beyond the necessary amounts.
In the field of oil production, and in many other commercial fields of interest today, it is desirable to meter relatively small quantities of chemical additives, continuously, over a relatively long period of time. Experience with low flow, high pressure injection systems, in particular, has indicated the need for improved flow meters.
With regard to flow metering in general, a variety of flow meter devices have been proposed. For example, a manual sight glass method employs a sight glass between a source of fluid to be pumped, upstream of a pump which directs that fluid to its desired destination. A valve is provided between the source of fluid and the sight glass. In operation, the pump is energized and the valve is open so as to allow fluid to fill the sight glass. The sight glass is provided with two markings, one above the other and the valve is closed when the level in the sight glass approaches the upper marking. The time and sight glass level are recorded and level in the sight glass is allowed to drop to the lower mark, when the time and level are again recorded. An average flow rate is calculated by dividing the difference in volume in the sight glass between the two markings, and the time required for the fluid to drop from the higher mark to the lower mark in the sight glass.